Thein Separator/PVC Pipe Question

[Michael MacDonald]

I am building a separator... 30-gal metal trash can; mdf for top and baffle... went to HD today to get the entry and exit piping... the 4-inch PVC is WAY TO LARGE for the flexible tube and compression clamps I have... so I picked up the 3-inch street elbow for entry and a small segment for the center exit pipe... I think the 3-inch pipe has nearly the same external diameter where it flares out for joints as needed by my flexible dust hose...

Going from the 4-inch flexible hose to the 3 inch PVC pipe... will that have an significant impact on my air flow? is it a bad idea? If so, I suppose I can got to Rockler to get actual dust control products...

Odd, but the Thein instructions I had specified 4-inch piping... don't see how that could have worked.

[Don Alexander]

i don't know the exact numbers but 4" pipe would have significantly more airflow than 3"

what kind of dust collector do you have ? don't think i have ever seen 1 with 3" inlet sounds more like a vac of some brand or other

[Michael MacDonald]

my DC is a 1 HP system from Harbor Freight... it is the mini, red DC... about 900 CFM. it is 4 inches, and I use 4-inch flex hose from Rockler... which fits right over the adapter on the DC.

So the 3-inch PVC pipe is a step down, but the outside dimenensino of the 4-inch pipe would never have fit the 4-inch flex hose. Or at least the 4-inch dust coupler (also from Rockler) I took to HD fit inside the 4-inch PVC with room to spare...

[Don Alexander]

you need a connector piece that goes inside the 4" pipe and the 4" flex
personally i would not even consider choking the airflow with a 3" section or connector just my 2 cents for whats its worth

[Michael MacDonald]

Maybe an additional comment is required to 'splain. I went to HD and looked through the entier plumbing section at the 4-inch PVC. Some 90-degree elbows had two flared ends, and some were street elbows with only one flared edge... I brough a 4-inch coupler (from Rockler... specifically for DC) for comparison, and when I held it up to the flared edge of the 4-inch pipe, it fit inside the PVC pipe with room to spare... when I held the 4-inch coupler up to the 3-inch PVC pipe's flared end, it was about the same size...

what is wrong with this... perhaps I was supposed to cut off the flared end... not sure that would have made much of a difference. No doubt the 4-inch PVC is four inches inside, but the outside is way more than four inches given the thickness of the pipe. So my 4-inch flex hose would never fit on it...

[Michael MacDonald]

so you are saying an adapter is required... hmmm. I assume others have done this, what adapter would I get? I didn't see anything usable at HD...

yes, I was worried that going from the 4-inch hose to the 3-inch pipe would be a bad idea.

Perhaps I should just go to Rockler tomorrow and get an elbow and nipple made for dust...

[Rob Wright]

Could you be looking at schd 40 pipe and not the preferred and cheaper 4" Sewer and Drain (S&D) or 3034 SDR 35 pipe that has a much thinner wall?

[Michael MacDonald]

Could you be looking at schd 40 pipe and not the preferred and cheaper 4" Sewer and Drain (S&D) or 3034 SDR 35 pipe that has a much thinner wall?

Rob -- perhas you are on to something... back to HD for me? Attached are pics of the 3-inch pipe up against my 4-inch-to-2.5 inch DC hose coupler. I don't know piping, apparently.

[Michael MacDonald]

I was researching and came across this link...

http://www.cgallery.com/smf/index.php?topic=140.0
http://www.youtube.com/watch?v=24gFgttTub0


discussion and resulting actual video proving that a 4" hose fits on a 4" S&D pipe.

(sorry if not supposed to post these types of links)

I think I am just using the wrong pipe. Back to borg to try again.

For those who love to hate borg, I had the complete and enthusiastic support and help from a borg employee for this purchase. Don't know how it went wrong. ha.

[Rick Markham]

You can always use a 4"to 4" connector for HVAC that they sell to connect two sections of 4" duct work together, the connector slides into the PVC and the flex hose slides over the outside

[Bruce Wrenn]

At HD's in our area, sch 20 pipe and fittings are located in the rear of the garden center, not plumbing. But the fitting you need to get from 4" sch 20 to 4" flex hose is located at Lowes. It's a 4" sch 20 X 3" sch 40 PVC adapter. The flex will slide right over the 3" side. Inside the 3" side is a molding in stop ring, which limits the depth you can insert the 3" pipe. I use a long pattern bit in the router to remove it. Google Phil Thein, and look at my post over at NC Woodworker, "Another Vote for Phil Thein's Baffle."

[Lee Schierer]

i don't know the exact numbers but 4" pipe would have significantly more airflow than 3"

what kind of dust collector do you have ? don't think i have ever seen 1 with 3" inlet sounds more like a vac of some brand or other

A 4" pipe has about 70% more cross-sectional area than a 3" pipe so it has about 70% more air flow.

[Michael MacDonald]

I returned the 3-inch pipe this morning... discovered that the sched 20 piping is in fact outside in the garden section. The HD I went to had slim pickens for the product... so I came away empty handed...

Ah well, at least I didn't cut my holes based on the sched 40 pipe and get the holes too big.

This has been educational.

[Myk Rian]

It would be nice if the DC ducting manufacturers took into account the size of PVC fittings and pipe. It's a constant battle trying to get things together.
I have some 4" to DC adapters from Woodcraft or Rockler (can't remember which) that don't come anywhere close to fitting ANY PVC pies or fittings. It's a real PITA. Oftentimes you need to wrap tape around things to get them fitted.

[Michael MacDonald]

ah... thanks for the comment Myk... I thought it was just me. Sometimes I make these things difficult. Like not figuring out I was using schedule 40 PVC and that the schedule 20 PVC was hidden in the garden section, where it could easily be found by anyone looking for plumbing pipes.